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Large Green Elbaite Tourmaline in Muscovite Specimen, South Dakota. From the old Bob Ingersoll Mine, Keystone, South Dakota.
The Black Hills Region, especially the central area of granitic uplift, is well known historically for great pegmatite mines, and is famous for gem rose quartz, tourmaline, beryl, spodumene, apatite, and many other minerals. Black tourmaline is abundant, but only a few localities are known for their lithia (elbaite) varieties. Chief among them is the Ingersoll, with abundant green and blue tourmalines, and a few scattered pink or olive crystals. The pegmatite did not pocket (in fact none of the Hills pegs did so really) so gem material is rare, and crystals seldom showed good terminations. Most of the samples show the crystals "frozen" in the quartz, muscovite mica, or feldspar. But the elbaites from here actually do get a bit gemmy. Clean gems up to 1/4 ct or even more have actually been fashioned from them, and many crystals do have small gem areas. Colors are an attractive shade.
This dump was a great place to rockhound for many years, but has been closed for awhile now due to vandalism and liability issues. Unfortunate, but that is how it has gone for many old famous mines. Hopefully it will someday be opened up again to fee collecting.
This attractive specimen is ~ 6 inches long by 2.25" by 2", quite large for the locale. The largest tourmaline is cracked, but about an inch wide. I have only ever had one good specimen larger from there, and it is still in my personal collection.
